The present invention relates to methods and materials for joining sections of flexible tubing together to form continuous lengths for various applications, especially, for example, casings for packaging food products like sausages, meats, cheeses and the like.
Tubular food casings, and more particularly, sausage casings like those made of regenerated cellulose and collagen have been widely used in processing frankfurters, bolognas, salamis, hams, etc. Tubular casings of various lengths are manufactured, for instance, by extruding viscose into a fibrous web which is then regenerated in a coagulating bath. The regenerated tubular material is washed to remove by-products, further treated and rolled flat onto large reels. In some instances, the casing is dried and shirred into tubular strands, or alternatively, left unshirred with sufficient water, placticizer, etc., such that further soaking need not be performed prior to stuffing by food processors. In either instance, a casing reel may contain several lengths of flat reelstock totaling several hundred feet.
The optimum length of continuous casing will vary depending on the particular apparatus, e.g. shirring, filling, employed. In general however, short lengths of casing will be inefficient, necessitating frequent stoppages of automated equipment to allow time to thread a new section of casing through the apparatus. For this reason, it has been found highly desirable to join or splice the end of one tubular casing to the beginning of a new section of tubular casing before the end of the first section begins its passage through the apparatus. The end portion of first section will then serve to pull the first section of the newly spliced section through the apparatus. In this manner, the need for frequent rethreading of the apparatus and restoring the cycle after each short length of casing material is run through can be avoided.
Various methods and materials have been proposed for splicing tubular casings. For example, U.S. Pat. No. 4,032,176 discloses several methods for assembling lengths of tubular casings end-to-end using pressure sensitive adhesive strips. It has been found, however, that unless splices are bonded with strips which are sealed with appropriate heat and pressure the frequency of joint separation can increase significantly, especially with casings having high moisture levels. Pressure sensitive adhesives do not form fully cured bonds, but instead, remain tacky. Consequently, such joints are not completely reliable, particularly since they must be machinable, remain intact when wet and be able to withstand the forces generated by stuffing equipment.
U.S. Pat. No. 2,631,509 discloses a method of making tubular articles from a continuous sheet which is drawn through a tube forming guide. As the tube is formed a lapped edge is made and a bead of thermoplastic material simultaneously deposited therebetween. The edge is sealed under heat and pressure. U.S. Pat. Nos. 3,560,223 and 3,669,692 disclose the fabrication of tubular articles from flat reelstock. The latter patents, however, relate specifically to casings for liver sausage, and therefore, have surfaces coated with saran polymer. In each of the immediate foregoing patents, the edges of the tubes are sealed without splicing tape. That is, the heat sealed joints of the prior art casings are bonded with an adhesive only which is non-supportive. The absence of a backing for the adhesive diminishes the machinability of the bonded joint especially when wet, and therefore, overall reliability is also diminished. Accordingly, there is a need for improved methods and materials for splicing tubular food casings together, and particularly, for the newer premoisturized casings prepared by manufacturers in ready-to-stuff condition with at least about 20% moisture content based on total casing weight. They would include premoisturized casings, for instance, even to gel state water content.